Environmentally-friendly vehicles are important on which survival of future motor industry is dependent. Vehicle manufacturers are focusing on development of environmentally-friendly vehicles so as to meet environment and fuel consumption regulations. The vehicle makers have been developing future vehicles such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell electric vehicles (FCEV).
Since the future vehicles have technical restrictions such as weight and cost, the vehicle manufacturers are forced to regularly follow up for meeting exhaust gas regulations and improving fuel consumption performance and are competing desperately to commercialize the hybrid electric vehicles into practical use.
The hybrid electric vehicles are vehicles using more than two power sources, gasoline engines or diesel engines using fossil fuel and motor/generators driven by electrical energy are mainly used as the two power sources of the hybrid electric vehicles.
The hybrid electric vehicle uses the motor/generator having relatively low-speed torque characteristics as a main power source at low-speed and uses an engine having relatively high-speed torque characteristics as a main power source at high-speed.
Since the hybrid electric vehicle stops the engine using the fossil fuel and uses the motor/generator at a low-speed region, fuel consumption may be improved and exhaust gas may be reduced.
The power transmission system of a hybrid electric vehicle is classified into a single-mode type and a multi-mode type.
Although a torque delivery apparatus such as a clutch or a brake for shift control is not necessary, fuel consumption is high due to deterioration of efficiency at a high-speed region and an additional torque multiplication device is required for a large vehicle according to the single-mode type. Since the multi-mode type has high efficiency at the high-speed region and is able to multiply torque autonomously, the multi-mode type is applied as the power transmission system of a hybrid electric vehicle, which has been under continuous investigation.
The power transmission system of the multi-mode type includes a plurality of planetary gear sets, a plurality of motor/generators, a plurality of torque delivery apparatus controlling rotation elements of the planetary gear sets, and a battery used as a power source of the motor/generators.
The power transmission system of the multi-mode type has different operating mechanisms depending on connections of the planetary gear sets, the motor/generators, and the torque delivery apparatus.
In addition, the power transmission system of the multi-mode type has different features such as durability, power delivery efficiency, and size depending on the connections of the planetary gear sets, the motor/generators, and the torque delivery apparatus. Therefore, designs for the connection structure of the power transmission system of a hybrid electric vehicle have been under continuous investigation to achieve robust and compact power transmission system having no power loss.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.